1. Field of the Invention
This invention relates to voltage comparator circuits and more particularly to a high-gain voltage comparator circuit suitable for manufacture in integrated circuit form having hysteresis associated therewith which is generated internally to the comparator circuit.
2. Description of the Prior Art
High gain integrated differential comparison amplifier circuits for providing output level states indicative of the magnitude of an input differential signal supplied thereto and having differential-to-single-ended converter circuits associated therewith are well known in the art. For instance, U.S. Pat. Nos. 3,649,846 and 3,872,323 describe such comparison circuits.
Generally, it is desirous to have any input offset voltage of the comparison amplifier circuit at zero so that as the magnitude of the differential input signal passes through the zero threshold level either in a positive or negative sense, the output of the comparison amplifier circuit is caused to switch between two output level states. However, some prior art comparison amplifier circuits of the type aforedescribed have a serious problem if they are to be utilized in a very high noise environment wherein relatively high noise transients may be generated. For example, if a noise transient occurs at or near the time that the differential input signal crosses through the zero threshold level the output of the comparison amplifier circuit can be caused to erroneously switch output states due to the noise transients as generally is understood.
To overcome the problems due to noise transients, some contemporary comparison amplifier circuits employ hysteresis. Typically the hysteresis is generated externally to the operation of the comparator circuit by circuitry which is responsive to the output from the comparator circuit switching states.
It may be desirous to have a comparison amplifier circuit capable of generating hysteresis internal to the comparison circuit and for allowing switching of the output of the comparison circuit between two output level states only after hysteresis has already been initiated internally to the circuit.